This invention relates generally to apparatus for expanding tubes into the plates or headers of heat exchangers or the like. More particularly, but not by way of limitation, this invention relates to an improved expander wherein the expander is permitted to move longitudinally with respect to the tube during the expanding operation.
In the manufacture of tube-type heat exchangers, it has been standard practice to roll or expand the tubing which extends through the heat exchanger header into tight sealing engagement therewith. Most tube expanders have the expanding rollers skewed slightly relative to the longitudinal axis of the tubing and expander so that they tend to feed or pull themselves into the tube as the expander is being rotated. One such expander is illustrated in U.S. Pat. No. 3,854,314 issued Dec. 17, 1974, to Paul Warren Martin.
Normally such expanders are prevented from moving longitudinally with respect to the tube, except in incremental steps as provided by the feeding devices used when rolling tubes in thick headers. Drift rolling, that is permitting the expander to move longitudinally during rolling, has been attempted manually. This manual procedure has not been successful because an operator cannot hold the expander to a constant preselected rolling interval. As a result, the expander rollers are not in engagement with the same quantity of tube material to be expanded or displaced and the interior of the tube, after rolling, is stepped rather than smooth as desired.
While such expanders have operated satisfactorily, they do tend to extrude the metal of the tube as it is being expanded toward the front of the header or tube sheet as well as toward the rear of the tube sheet since the thickness of the tube is changed by the rollling or expanding operation. In some applications, it is desirable to weld or otherwise affix the ends of the tubes to the tube sheet prior to the expanding operation. In this case, extreme forces are generated in the tubes while the tubes are being expanded.
An object of this invention is to provide an improved tube expander that avoids pulling the tube material toward the face of the header and thus eliminates the forces generated as a result of the extrusion of the tube material.
Another object of the invention is to provide an improved tubing expander wherein relative axial movement can occur between the expander and the tube during the rolling operation to avoid the imposition of axial forces toward the face of the header during the rolling operation and to provide a more uniform deformation.